Reading Your Joints

A good solder joint is inspectable with your eyes. Learn the looks and you'll diagnose your own work.

The good joint

• Shiny (lead solder) — smooth, reflective surface
• Concave — curves inward like a tiny volcano, lead visible but covered
• Wetted — solder flows smoothly onto both pad and lead, no sharp edges where it "refused" to stick

If it looks like a tiny Hershey's Kiss that flowed into place, you did it right.

The bad joints

Problem	Looks like	Cause	Fix
Cold joint	Dull, gray, lumpy or cracked	Parts moved while cooling, or never got hot enough	Reheat fully until it flows, hold still
Insufficient wetting	Solder balled up, not flowing onto pad	Pad/lead not hot enough; dirty surfaces	Clean, reheat the parts, feed fresh solder
Solder bridge	Blob connecting two adjacent pads/pins	Too much solder	Wick it away with desoldering braid
Too much solder	Big ball hiding the lead	Overfeeding	It's ugly but often works; wick the excess
Too little	Lead barely covered, joint starved	Underfeeding	Add a touch more to a reheated joint
Lifted pad	Copper pad peeling off the board	Overheated (too long, too hot)	Hard to fix — prevention: 3–5 seconds max

The magnifier test

A $10 helping-hands magnifier (or your phone's camera zoomed in) reveals what naked eyes miss: hairline cracks in cold joints, bridges between fine-pitch pins. Inspect, don't assume — especially before powering a board for the first time.

Fixing mistakes

• Desoldering braid (wick): copper braid that drinks molten solder when heated — for bridges and excess.
• Solder sucker: spring-loaded vacuum that inhales molten solder — for clearing holes.
• Just reheat: most ugly-but-connected joints can be reheated with a touch of fresh solder (fresh rosin core brings fresh flux) and they'll flow into shape.

The rule: a joint you can see through to both metals, shiny and still, is a joint you can trust. When in doubt, reheat it — rework is normal, not failure.

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